The alligator and its allies

by A. M. Reese

A short distance caudad to the iliac veins, each epigastric receives one or two fairly large branches from the pelvic region, called by Bronn the ischiadic veins, is. Caudad to the ischiadics and dorsal to the cloaca, each epigastric is united with a short but wide renal portal or renal advehente vein, rp, leading to the posterior border of its respective kidney and receiving, on the way, a short branch from the pelvic region, shown just cephalad to the reference lines rt and rp.

Very close to its junction with the renal portals each epigastric gives off a small branch which unites with its fellow of the opposite side to form a median vein, rt, the rectal leading from the posterior part of the large intestine. A very short distance caudal to these last veins, in the region just dorsal to the anal opening, the epigastrics are formed by the division of the caudal vein, cv, which, of course, brings blood from the tail and is, on account of the large size of that organ, of considerable caliber.

The Anterior Venæ Cavæ and their Branches.

The entrance of the precaval veins into the heart was mentioned above; their branches, in order from the heart cephalad, will now be described. Since the two precavæ are alike, it will be necessary to describe the branches of only one side of the body. After leaving the heart, the precava may be traced forward, for a short distance, at the side of the trachea and œsophagus, as a wide, thin-walled trunk, [Fig. 60], vca. The first tributaries that it receives are the internal mammary and vertebral veins, which join it at the base of the neck at almost the same place.

The internal mammary, [Fig. 60], im, is a rather small vein, bringing blood from the ventral wall of the thorax. It may be followed along the inner surface of the ribs, near the sternum, in company with its corresponding artery.

The vertebral vein, [Fig. 60], v, is also of small diameter and extends to the dorsal body wall near the spinal column, from which region it returns blood to the anterior vena cava; it is drawn too large in the figure.

Fig. 60. The veins of the anterior region of the Florida alligator. The veins of the left foreleg are shown at A.—For lettering, see [pages 224-25].

Just cephalad to the vertebral and internal mammary, the internal jugular, j, enters the precava. The internal jugular may be followed directly forward, close to the side of the trachea and œsophagus, from which it receives numerous branches. Near its point of entrance to, or rather exit from, the skull, it anastomoses, by two or three short branches, with the external jugular, ej, to be described later. Its distribution in the cranial cavity could not be determined in the available material. At the point of entry of the internal jugular the precava passes laterad for a short distance and then divides into two more or less equal branches, the above-mentioned external jugular, ej, and the subclavian, s, of which the latter will first be described.

The subclavian, s, of course, returns blood from the regions of the shoulder and arm. On reaching the body wall, where it might be called the axillary, ax, it receives, on its posterior side, a large thoracic vein, t, which returns blood from the thorax, shoulder, and skin. The thoracic receives a branch from the posterior surface of the arm, which might be called the postbrachial, pb; this postbrachial may be traced, as a rather small vessel, to the hand; at the elbow it is connected, by one or more small branches, with the brachial.